Modern vehicle systems are made up of a multitude of system components that are networked and interact with each other. Due to safety requirements, for example, inhibit relations are frequently defined between certain vehicle components. The inhibit relations are activated and deactivated as a function of diagnosis states.
That is to say, depending on the states of individual diagnoses, certain functionalities may not become active in the vehicle due to the inhibition. According to certain conventional systems, such inhibit relations in vehicle systems are controlled via a DSM (Diagnostic System Manager) with the aid of a so-called DINH (Diagnostic Inhibit Handler). Depending on the particular state of a DFC (Diagnostic Fault Check), so-called FIDs (function identifiers) are enabled or inhibited. In view of the multitude of components in modern vehicle systems, which, furthermore, feature a high degree of cross-linking, it may happen that corresponding functionalities lead to a cyclical chain of inhibitions, so that none of the FIDs in a cycle is enabled anymore. Such a state is usually referred to as deadlock.
As a rule, a deadlock can no longer be reversed and must consequently be prevented in advance by an appropriate arrangement of the associated inhibit relations.
Therefore, an aspect of the so-called DSM plausibilization that is involved in this context to detect critical inhibit relations and to identify which ones of them could potentially lead to a deadlock. Hereinafter, such critical inhibit relations are referred to as “deadlock-critical”.
For illustration purposes, FIG. 1 shows a cycle denoted by 100 as a whole, which includes a deadlock. The cycle is made up of previously elucidated DFCs, denoted by DFC_1 and DFC_2 in this instance, and also of the corresponding FID_1 and FID_2. Here, the FIDs, indicated by arrows 110 and 111, calculate states of the associated DFCs. The DFCs, illustrated by arrows 120 and 121, cause a release or inhibition of the individually post-connected FIDs. As symbolized by the double-crossed arrows 120, 121 in FIG. 1, the particular DFCs are in an inhibit state. In the state of FIG. 1, both DFC_1 and DFC_2 wait for a release by the associated FIDs, which does not take place, however, because the FID in turn is inhibited by the DFCs immediately upstream.
For the purpose of determining deadlock-critical relations between components of a vehicle system, it is conventional to arrange a graph which reproduces the vehicle system and has nodes and edges in accordance with conventional graph-theory rules, the nodes and edges representing the components and their relations.
According to certain conventional systems, all paths in the graph that connect the system components or the nodes by which they are symbolized, are searched in order to discover deadlock-critical cycles. Corresponding methods are described in German Published Patent Application No. 197 230 079, U.S. Pat. No. 6,223,200, U.S. Pat. No. 5,832,484, and Japanese Published Patent Application No. 63-103934, for example.
However, conventional methods have the disadvantage that, because of the large number of paths to be checked, the run time of a corresponding algorithm is unacceptably long (several days). In contrast, an alternative according to which only the shortest paths in a corresponding graph would be checked would have the result that perhaps a non-critical (shorter) cycle is found and output for a node despite the fact that a critical (longer) cycle exists in addition. The critical cycle would therefore not be found and in practice could cause a deadlock.
Therefore, it is desirable to provide an optimized method for determining deadlock-critical relations, which has acceptable run times and which makes it possible to determine the largest and most complete number of deadlock-critical relations possible, critical cycles being found before less critical cycles.